This proposal aims at a better understanding of the interrelationships between thermal acclimation, membranes, and aging. The nematode Caenorhabditis elegans will be used because of the feasibility of using genetic analysis in this organism. Changes in membrane properties such as viscosity and critical temperatures of enzyme activities will be determined as a function of thermal acclimation and of age. Mutations affecting thermal acclimation will be sought and the effects of these mutations on membrane properties and aging will be determined.